Pathophysiology of patent ductus arteriosus (PDA)
In the normal fetus, the ductus arteriosus is open, in which non-oxygenated venous blood enters the pulmonary artery from the fetal right ventricle, then bypasses the lungs (which are not yet open and in a nonfunctional state during fetal life) and enters directly into the descending aorta, from which it is oxygenated through the placenta. Vasoconstriction leading to functional closure of the ductus arteriosus occurs soon after birth in full-term newborns, while anatomic closure produced by intimal and fibrous tissue proliferation takes several weeks to complete. From 2 months to 1 year of age after birth, the vast majority have closed. those who remain unoccluded after 1 year of age are considered to have an unoccluded ductus arteriosus.
Isolated PDAs are classified according to the degree of left-to-right shunt, i.e., the size and length of the catheter and the difference in vascular resistance between the pulmonary and body circulations.
1. Resting PDA: Small PDA that is detected only on subclinical examination, such as ultrasonography.
2.Small PDA: with a continuous murmur and Qp/Qs <1.5/1.0 (pulmonary artery/aortic blood flow);
3, moderate PDA: with continuous murmur, Qp/Qs=1.5~2.2/1.0;
4, large PDA: Qp/Qs>2.2/1.0;
5, Eisenmenger syndrome: presence of continuous murmur; severe pulmonary hypertension, differential hypoxemia, differential cyanosis.
II. Natural history of ductus arteriosus closure
1.Arterial ductus in preterm infants: due to underdevelopment, the arterial ductus in preterm infants is delayed in life closure.
2.Arterial duct in term newborns: Some term newborns have persistent non-closure of the ductus arteriosus due to relative hypoxemia. The causes of these hypoxaemia include: higher altitude at birth; congenital anomalies causing hypoxemia; congenital anomalies in the arterial duct blood supply to the body circulation, such as left ventricular dysplasia syndrome, aortic block or aortic constriction.
3. Arterial catheter in children or adults.
The resting type is found on ultrasonography without long-term complications, but there are exceptions, such as inaudible murmurs due to obesity or body wall factors;
Small PDA: with a small shunt does not cause significant hemodynamic disturbances but has the underlying condition of endocarditis;
Moderate PDA: increases the left ventricular volume load, leading to left ventricular dilatation and insufficiency, and eventually to atrial fibrillation;
Large PDA: leads to excessive volume load and occurs with a stepwise increase in pulmonary artery pressure, leading to irreversible pulmonary vascular changes (Eisenmenger syndrome).
Third, the treatment of arteriovenous catheter failure
1.Transcatheter treatment.
For <8 mm can be blocked by transcatheter implantation of devices, has been for 30 years, the effect is safe and effective. After 1-year follow-up after device implantation, more than 85% can be completely closed, with a mortality rate of <1%;
2.Surgical treatment.
When the PDA is large, or when device blocking is not possible, surgical treatment is considered. Surgical treatment of PDA has a history of 60 years, and the postoperative closure rate is higher than that of catheterization, but the mortality and disability rates are slightly higher. The rate of clinical closure (no shunt on physical examination) right after surgery is up to 95%. Surgical closure is a low-risk treatment for children. The mortality rate in adults is 1 to 3.5%, mainly due to pulmonary hypertension and abnormal ductus arteriosus morphology.
IV. Fertility problems in women with ductal incompetence
Women with resting or asymptomatic small PDA can tolerate pregnancy; pregnancy in women with hemodynamic abnormalities can induce or worsen heart failure; Eisenmenger syndrome is contraindicated by high mortality in pregnancy;
V. Follow-up issues of arteriovenous catheterization
1. Device occlusion or surgical treatment should be followed up regularly to detect possible recanalization of the closed catheter;
2. Transthoracic ultrasound can detect resting residual shunts;
3. The risk of advanced endocarditis due to residual shunts at clinical rest after device occlusion or surgery is low and requires a 6-month follow-up.